Many vehicles require a parking brake that provides high braking torque while requiring minimal effort by a user. These vehicles are typically heavier vehicles, such as, for example, construction vehicles, agricultural vehicles, utility vehicles, and golf care turf care machines. One type of parking brake often used on such vehicles is a caliper brake, where opposing calipers have a gap therebetween and apply a braking force to a rotating rotor positioned in the gap. These caliper brakes can be mounted at the wheel of a vehicle, or alternatively can be mounted elsewhere in the drive train of the vehicle. A number of mechanisms can be used to actuate the caliper brake, including a ball ramp actuation mechanism, which is often preferred because it is relatively simple in design, reliable, and easy to service and operate. However, known ball ramp actuation mechanisms for caliper brakes suffer from a number of disadvantages generally and specifically in high torque applications.
In high torque parking brakes of heavy vehicles, the input force supplied to the manually activated brake actuation mechanism is limited by the capabilities of the human user. Thus, the mechanical advantage provided by the brake is critical in obtaining the necessary braking torque. Nevertheless, conventional caliper brake actuation mechanisms tend to be extremely inefficient, losing from between twenty to seventy percent of the input force to inefficiencies. These inefficiencies are largely a result of friction throughout the brake. Conventional caliper brake ball ramp actuation mechanisms also can be difficult to mount and install on or adjacent to the vehicle wheel. The ball ramp actuation mechanism includes a lever connected to a rotatable actuation mechanism, and the adjustability of the lever position, when installed, is limited by known designs. Lever position is important to allow cables and linkages to be easily secured to the lever to connect the manual input device to the brake.
One method of connecting a lever to a rotatable actuator in a ball ramp actuation mechanism is disclosed in U.S. Pat. No. 7,040,062 ('062 patent). This patent discloses a rotatable actuator and lever that are formed integrally as a single piece. The rotatable actuator includes ramped depressions that receive balls therein, the balls also being received in corresponding ramped depressions formed in a stationary actuator, as is known to those skilled in the art. Thus, the lever position is limited by the ball and depression positions, effectively limiting the lever to as few as three positions during installation. In addition, it is noted that the rotatable actuator of the device disclosed in the '062 patent presses against a washer, which helps to reduce friction slightly, but some friction related inefficiencies remain. While such a brake may be suitable for lower torque applications, such as in relatively light weight vehicles like golf carts, it is not suitable for the high torque applications contemplated by the present invention.
Another method of connecting a lever to a rotatable actuator in a ball ramp actuation mechanism is disclosed in U.S. Pat. No. 5,529,150 ('150 patent). The rotatable actuator and the lever each include splined surfaces that, when engaged, rotationally couple the lever to the rotatable actuator. Like the '062 patent, the rotatable actuator and a stationary actuator each include ramped depressions that receive balls therein, and rotation of the rotatable actuator causes the balls to travel up the ramps, thereby generating axial movement of the rotatable actuator. The splined attachment of the lever to the rotatable actuator offers greater adjustability than the '062 patent device, but is still limited to a finite number of locations. In addition, the spline teeth are a likely point of failure under high loads. It is also noted that manufacturing costs of the splined surfaces are relatively high, and the machining of the ramped ball depressions in the '150 device would be difficult and expensive as well due to their proximity to other components of the brake.
Thus, there is a need for an improved ball ramp caliper brake that alleviates one or more of the above mentioned deficiencies of the prior art.